10 replies to this topic

[Kachisa]

Hi All,

I got a mach number at PSV outlet nozzle  = 1 but 0,7 at pipe outlet.

It is ok ?

 

Thank you

[Bobby Strain]

We have no idea what you are doing. Maybe you can provide some information so we might help.

 

Bobby

[Kachisa]

Dear Mr. Bobby,

 

API recommend to limit mach number of pipe oulet to 0,7 but it does not talk about PSV outlet nozzle.

 

I am checking an existing PSV, and I got a Mach Number at PSV outlet nozzle = 1.

[fallah]

 

I got a mach number at PSV outlet nozzle  = 1 but 0,7 at pipe outlet.

It is ok ?

 

Kachisa,

 

It could be possible in critical flow through the PSV means having sonic flow in PSV orifice which will result in a subsonic flow through the relevant tail pipe due to the back pressure...

[Kachisa]

Thanks Mr. Fallah for your comment. 

I got clearly your idea and I totally agree with you.

My worry is not the result, it is rather sound criteria.

 

Another point : the PSV is sized only for fire case.

As fire flowrate is very important, I will use 2 PSV. 

My question is : if these PSV should be staggered ?

I see that is not necessary.

[fallah]

Thanks Mr. Fallah for your comment. 

I got clearly your idea and I totally agree with you.

My worry is not the result, it is rather sound criteria.

 

Another point : the PSV is sized only for fire case.

As fire flowrate is very important, I will use 2 PSV. 

My question is : if these PSV should be staggered ?

I see that is not necessary.

 

If you have to use multiple PSV's to handle the whole relif load they should be staggered.either in fire case or in another case...

[Kachisa]

 

If you have to use multiple PSV's to handle the whole relif load they should be staggered.either in fire case or in another case...

 

 

Thanks Mr. Fallah,

2 PSV in service : 1 PSV * 100% + 1 PSV * 105 %

How about the spare PSV, it is set at 100% or 105%, and why ?

[fallah]

 

2 PSV in service : 1 PSV * 100% + 1 PSV * 105 %

How about the spare PSV, it is set at 100% or 105%, and why ?

 

 

Spare PSV should be set same as the main PSV...because it's not intended to be operated simultaneous with the main PSV ..

[Kachisa]

Thank you Mr. Fallah,

But PSV 105% may fail ? It is a recommendation from API ?

[fallah]

 

But PSV 105% may fail ? It is a recommendation from API ?

 

Your statement isn't clear; please explain...

[demank]

For Fire Case PSV, it is not necessary to install spare PSV.